1. Field of the Invention
The present invention relates to a signal detecting device and related method, more particularly, to a device of a communication system for detecting signal strength and related method.
2. Description of the Prior Art
Generally, the automatic gain control (AGC) has been used in a radio frequency (RF) receiver to adjust strength of received signals at the analog front-end so that the received signals do not suffer much distortion at a stage of converting into back-end digital signals. Before adjusting gains, the receiver must measure the strength of received signals in order to get the appropriate range for signal adjustment.
The RF receiver normally includes one or several amplifiers with variable gains and analog to digital converters with a range of linear transformation. The RF receiver adjusts amplifier gains according to strength of detected signals to maintain the signals received by analog to digital converters within the range of the transformation to avoid distortion.
The typical method of signal strength detection is to detect strength of signals whose frequencies have been downed to an intermediate frequency band or near baseband frequency band and then to adjust corresponding amplifier gains according to the detected strengths. U.S. Pat. No. 7,212,798 discloses, in FIG. 2, a signal strength detecting device detecting strengths of the received signals at three stages from the intermediate to low frequency stages in the signal receiving path, i.e. the analog RSSI detectors 227 and 217 and the digital measuring logic circuit 231. However, detecting signal strength at the low frequency (e.g. 200 KHz) requires long signal settling time and ripple effect is more severe in the low frequency signals. In addition, the signal strength detecting device usually demands capacitors with larger capacitance to reduce ripples, thereby occupying larger circuit area.